Plasma processing apparatus and method with controlled biasing functions

ABSTRACT

A plasma processing apparatus including: a phase controller for controlling a phase difference between biasing power supplied to the antenna biasing electrode and biasing power supplied to the substrate electrode to have a difference of 180°±45°; wherein the biasing power supplied to the antenna biasing electrode and the biasing power supplied to the substrate electrode have a same frequency, which same frequency is lower than a frequency of the RF power for plasma generation. A plurality of filters is included, to perform a variety of filtering.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 11/053,236, filedFeb. 9, 2005, which is a divisional of U.S. application Ser. No.09/946,491, filed Sep. 6, 2001 (now U.S. Pat. No. 6,875,366). Thisapplication relates to and claims priority from Japanese PatentApplication No. 2000-276667, filed on Sep. 12, 2000. The entirety of thecontents and subject matter of all of the above is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to plasma processing apparatus and method,and particularly to a plasma processing apparatus and method suitablefor making surface treatment of a sample such as a semiconductor deviceby use of plasma.

2. Description of the Related Art

In the plasma etching process, the processing gas is ionized to beactivated for fast processing, and radio frequency (RF) biasing power issupplied to a sample to be processed (or a processed sample) so that theions in the plasma can be incident perpendicularly to the sample to beprocessed, thereby achieving high-precision etching for anisotropicshape and so on.

A plasma processing apparatus for this purpose is disclosed in Yokogawaet al U.S. Pat. No. 5,891,252. This apparatus, as described in thatdocument, has an air-core coil provided on the outer periphery of theoutside of a vacuum vessel, and a circular conductor plate provided tooppose a wafer stage within the vacuum vessel. In addition, an UHF bandpower supply and a first RF power supply are connected to the circularconductor plate, while a second RF power supply is connected to thewafer stage, so that an electric field of UHF band and anther electricfield of frequencies different from the UHF band are appliedsuperimposed upon each other to the circular conductor plate. Thus,plasma is generated by use of electron cyclotron resonance due to themutual action between the electromagnetic waves from the UHF band powersupply and the magnetic field from the air-core coil. The superimposedRF voltage from the first RF power supply increases the bias voltage tothe circular conductor plate so that the circular conductor plate andthe plasma can be reacted to more produce activated species thatcontribute to the etching, and the second RF power supply connected tothe wafer stage controls the energy of ions within the plasma, incidentto the sample.

Also, it is generally known that in a plasma with a static magneticfield applied, the impedance of the plasma perpendicular to the magneticfiled is larger than that parallel to the field as described in“DIFFUSION ACROSS A MAGNETIC FIELD 5.5” in “INTRODUCTION TO PLASMAPHYSICS AND CONTROLLED FUSION” written by F. F. Chen, and published byPlenum Press, PP. 169-172, 1974.

SUMMARY OF THE INVENTION

In the above plasma processing apparatus, since the electric path of theRF power supplied to the sample to be processed propagates to cross themagnetic field, the impedance of the plasma perpendicular to thismagnetic field may act to form a potential distribution in the surfaceof the sample to be processed, which causes charging damage. Inaddition, the energy of ions incident to the sample to be processed isdetermined by the self-bias potential due to the biasing power fed tothe sample to be processed, and there is the problem that the efficiencyof the bias application is reduced since the rate of the earth area tothe substrate electrode is decreased with the increase of the wafer sizetoward a large diameter.

Also, in the conventional apparatus, since the vacuum vessel isgrounded, the plasma is spread within the vacuum vessel of groundpotential, and diffused up to the outer peripheral region so that theplasma cannot be confined enough within the processing region of thevacuum vessel's inside. Therefore, in this apparatus, the inner wall ofthe vacuum vessel is sputtered, thereby increasing the amount of partialproduced.

In recent years, as the integration degree of semiconductor integratedcircuits has been increased, the thickness of, for example, the gateoxide film of MOS (Metal Oxide Semiconductor) as a typical example ofthe semiconductor device has been so decreased that the gate oxide filmmay cause dielectric breakdown (charging damage). Moreover, as the sizeof semiconductor devices has become very small, the mask selectivity asrepresented by SAC (Self Aligned Contact) about the processing precisionhas been requested to improve. Also, since the generation of particle orthe like within the apparatus reduces the yield and the operation rateof the apparatus, the apparatus with less particle produced is demanded.

It is the first object of the invention to provide a plasma processingmethod and apparatus capable of suppressing the charging damage in theplasma processing.

It is the second object of the invention to provide a plasma processingmethod and apparatus capable of high-precision surface treatment.

It is the third object of the invention to provide a plasma processingmethod and apparatus capable of reducing the amount of particleproduced.

It is the fourth object of the invention to provide a plasma processingmethod and apparatus capable of high throughput.

The first object can be achieved by providing an electrode opposite to asubstrate electrode on which a sample is placed; supplying RF power forplasma generation to the opposite electrode; and supplying, to both theelectrodes, other RF power having lower frequencies than the RF powerfor plasma generation and opposite phases.

The other RF power of opposite phases supplied to both the electrodeshave a phase difference of 180°±45°.

The other RF power of opposite phases supplied to both the electrodesalso have a phase difference of 180°±30°.

The other RF power supplied to both the electrodes have the samefrequency of 5 MHz or below.

The plasma is produced by use of RF power and magnetic field.

Moreover, the first object is achieved by providing an electrodeopposite to a substrate electrode on which a sample is placed; supplyingRF power for plasma generation to the opposite electrode; and supplying,to both the electrodes, other RF power having lower frequencies than theRF power for plasma generation, thereby forcing currents in the plasmato flow in the same direction between the electrodes, and therebychanging the orientation of the currents flowing in the same directionalternately toward one and the other of both the electrodes.

The frequencies of the other RF power applied to both the electrodes aremade equal to be 5 MHz or below.

The first object is also achieved by providing an electrode opposite toa substrate electrode on which a sample is placed; supplying RF powerfor plasma generation to the opposite electrode; and supplying, to boththe electrodes, other RF power having lower frequencies than the RFpower for plasma generation, thereby forcing the electrons and ions fromthe plasma to be incident to both the electrodes in the oppositedirections, respectively, and thereby alternately switching the oppositeincident directions of the electrons and ions from the plasma to boththe electrodes.

The frequencies of the other RF power applied to both the electrodes aremade equal to be 5 MHz or below.

The second object is achieved by providing an electrode opposite to asubstrate electrode on which a sample is placed; supplying RF power forplasma generation to the opposite electrode; and supplying, to both theelectrodes, other RF power having lower frequencies than the RF powerfor plasma generation, thereby, while the ions is being incident to oneof both the electrodes, forcing a number of electrons to be pulled intoward the other electrode, thereby repeating the incidence of ions andthe pulling-in of electrons alternately, and thereby forcing the biasvoltage waveforms produced on both the electrodes to be shifted towardthe negative voltage side, thus making an ion energy distribution inwhich the amount of high-energy ions is large.

The frequencies of the other RF power applied to both the electrodes aremade equal to be 5 MHz or below.

The third object is achieved by providing an electrode opposite to asubstrate electrode on which a sample is placed; supplying RF power forplasma generation to the opposite electrode; and supplying, to both theelectrodes, other RF power having lower frequencies than the RF powerfor plasma generation and opposite phases, thereby forcing either one ofboth the electrodes to always function as an earth electrode, therebypreventing the vacuum vessel from being grounded as viewed from theplasma.

The third object is also achieved by providing an electrode opposite toa substrate electrode on which a sample is placed; supplying RF powerfor plasma generation to the opposite electrode; and supplying, to boththe electrodes, other RF power having lower frequencies than the RFpower for plasma generation, thereby reducing the positive voltages ofthe bias voltages due to the RF voltages applied to both the electrodesto lower the plasma potential so that the potential difference is lowrelative to the inner wall of the vacuum vessel grounded, and therebysuppressing the ions in the plasma from making an impact to the innerwall surface of the vacuum vessel.

The fourth object is achieved by providing an electrode opposite to asubstrate electrode on which a sample is placed; supplying RF power forplasma generation to the opposite electrode; supplying, to both theelectrodes, other RF power having lower frequencies than the RF powerfor plasma generation and opposite phases during the processing of thesample; and supplying other RF power having the same phase to both theelectrodes during the cleaning of the chamber's inside.

In order to achieve these objects, according to an aspect of theinvention, the plasma processing apparatus includes a container of whichthe inside is controlled to have a predetermined pressure-reducedatmosphere; a substrate electrode provided within said container and onwhich a sample can be placed; an opposite electrode provided within thecontainer to oppose the substrate electrode; a plasma generating powersource connected to the opposite electrode to supply RF power theretoand to thereby generate the plasma; a plurality of biasing powersupplies connected to the substrate electrode and the opposite electrodeto supply thereto other RF power having lower frequencies than the RFpower for plasma generation; and a phase control for controlling thephases of the RF voltages from the plurality of biasing power supplies.

In the above apparatus, the phase control controls the phases of the RFvoltages to both electrodes to be opposite to each other.

The phase control also controls the phases of the RF voltages to bothelectrodes to be equal and opposite to each other.

The phases are controlled to have a difference of 0°±45° or 180°±45°.

The phases are also controlled to have a difference of 0°±30° or180°±30°.

The plurality of biasing power supplies generate RF power of the samefrequency of 5 MHz or below.

A field-generating coil is provided for producing magnetic field in thecontainer.

According to another aspect of the invention, the plasma processingapparatus includes a process chamber connected to a vacuum exhauster sothat the chamber's inside pressure can be reduced; a gas supplying unitfor supplying gas to the process chamber; a substrate electrode providedwithin the process chamber and on which a sample to be processed can beplaced; an antenna electrode provided to oppose the substrate electrodewithin the process chamber and from which electromagnetic waves forgenerating the plasma are radiated; a first RF power source connected tothe antenna electrode to supply thereto RF power for plasma generation;a second RF power supply connected to the substrate electrode; a thirdRF power supply connected to the antenna electrode; and a phase controlfor controlling the phases of the RF voltages from the second and thirdRF power supplies to be opposite to each other.

According to still another aspect of the invention, the plasmaprocessing apparatus has an electrode provided to oppose a substrateelectrode on which a sample is placed; supplies RF power for plasmageneration to the opposite electrode; supplies, to both electrodes,other RF power having lower frequencies than the RF power for plasmageneration and opposite phases; and produces a magnetic field havinglines of magnetic force passed through both electrodes.

The opposite phases of the RF power are set so that the self-biasvoltage difference in the surface of the sample is 5 V or below.

The opposite phases of the RF power are also set so that the self-biasvoltage difference in the surface of the sample is substantially 0 V.

According to the plasma processing of the invention, by controlling thephases of the RF power applied to the substrate electrode and theantenna electrode opposite to the substrate electrode, it is possible tolower the potential distribution in the surface of the sample to beprocessed due to the distribution (or uniformity) of the plasmacharacteristic, and to thereby suppressing the charging damage fromoccurring. Also, by controlling the phases of RF power, it is possibleto adjust the energy of ions incident to the sample to be processed, tomake etching of high aspect ratio, and to improve the mask selectivity.Therefore, high-precision etching can be performed. Moreover, bycontrolling the phases of the RF power, it is possible to suppress theplasma from being dispersed, and to reduce the amount of particles dueto the sputtering to the inner wall of the vacuum vessel and due to thereaction products attached to or detached from the inner wall. Thus, theyield can be improved, and the maintenance period of the apparatus canbe extended, so that the throughput can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinally cross-sectional view of an etching apparatusas the first embodiment of the invention.

FIG. 2 is a graph showing the relation of the voltage across the gateoxide film to the phase difference between RF voltages.

FIGS. 3A and 3B are diagrams showing the waveforms of voltages at thesubstrate/antenna electrodes when the bias voltages of the samefrequency are applied to the substrate electrode and antenna electrode.

FIGS. 4A, 4B and 4C are diagrams showing the relation of the RF voltagesapplied to the substrate electrode and antenna electrode and themovement of ions and electrons in the plasma.

FIG. 5 is a diagram showing the energy distribution of ions that areincident to the electrodes with the phase difference of voltages changedto be 0° and 180°.

FIG. 6 is a graph showing the relation of the ion saturated currentdensity of the outer periphery and the phase difference.

FIG. 7 is a graph showing the relation of the phase difference of biasvoltages and the self-bias voltage difference in the substrate surfacewith the magnetic field intensity changed.

DETAILED DESCRIPTION OF THE EMBODIMENTS

One embodiment of the invention will be described with reference toFIGS. 1 through 5. FIG. 1 is a longitudinally cross-sectional diagram ofthe etching apparatus as an example of the plasma processing apparatusto which the present invention is applied. A vacuum vessel 101 hasprovided on the upper opening side a cylindrical process container 102,a flat-shaped antenna electrode 103 of a conductor and a dielectricwindow 104 through which electromagnetic waves can be transmitted, so asto hermetically seal the top opening to form a process chamber insidethe container. A field-producing coil 105 is provided around the outsideof the process container 102 to surround the process chamber. Theantenna electrode 103 has a perforated structure for the supply ofetching gas from a gas feed unit 107 connected to the antenna electrode.In addition, below the vacuum vessel 101 there is provided a vacuumexhauster (not shown) that is connected via a vacuum vent 106 to thevessel.

A coaxial line 108 is provided on the top of the antenna electrode 103to be connected thereto, and the coaxial line 108 is further connectedvia a filter 109 and a matching circuit or box 110 to an RF power source111 (of, for example, 450 MHz in frequency) for plasma generation. Theantenna electrode 103 is also connected via the coaxial line 108, afilter 112 and a matching circuit or box 113 to an antenna biasing powersupply 114 (of, for example, 800 kHz in frequency). Here, the filter 109allows the RF power to be passed therethrough from the RF power source111, but effectively cuts off the biasing power from the antenna biasingpower supply 114. The filter 112 allows the biasing power to be passedtherethrough from the antenna biasing power supply, but effectively cutsoff the RF power from the RF power source 111.

A substrate electrode 115 which is a so-called “sample stage” on which asample 116 to be processed can be placed is provided on the bottom sideof the inside of the vacuum vessel 101. The substrate electrode 115 isconnected via a filter 117 and a matching circuit or box 118 to asubstrate biasing power supply 119 (of, for example, 800 kHz infrequency). The substrate electrode 115 is also connected via a filter120 to an electrostatic chuck power supply 121 for electrostatic suctionof the sample 116. Here, the filter 117 allows the biasing power to bepassed therethrough from the substrate biasing power supply 119, buteffectively cuts off the RF power from the RF power source 111. Althoughthe RF power is normally absorbed within the plasma, and thus does notflows to the substrate electrode 115 side, the filter 117 is providedfor safety's sake. The filter 120 allows the DC power to be passedtherethrough from the electrostatic chuck power supply 121, buteffectively cuts off the power from the RF power source 111, antennabiasing power supply 114 and substrate biasing power supply 119.

The antenna biasing power supply 114 and the substrate biasing powersupply 119 are connected to a phase controller 122 that controls thephases of the voltages from those power supplies 114, 119. In this case,the frequencies of the voltages from the power supplies 114, 119 are thesame.

The phase controller 122 responds to the voltage waveforms from thejunction between the filter 112 and matching circuit 113 on the antennabiasing power supply 114 side and from the junction between the filter117 and matching circuit 118 on the substrate biasing power supply 119side to produce signals with a small amplitude so that the desired phasedifference of those signals can be kept opposite, or 180°±45°, and tosupply those signals to the antenna biasing power supply 114 and thesubstrate biasing power supply 119, respectively. In this case, theantenna biasing power supply 114 and the substrate biasing power supplymay only function as amplifiers, respectively.

If the phase controller 122 responds to the voltage waveforms from thejunction between the filter 112 and matching circuit 113 on the antennabiasing power supply 114 side and from the junction between the filter117 and matching circuit 118 on the substrate biasing power supply 119side to produce only trigger signals that support the output timing ofthe power, the antenna biasing power supply 114 and the substratebiasing power supply 119 function as oscillators, respectively.

In the apparatus constructed as above, after the inside pressure of theprocess chamber is reduced by the vacuum exhauster (not shown), the gasfeed unit 107 supplies etching gas into the process chamber until thepressure within the chamber can be adjusted to be a desired value. Theoscillation output, or an RF power of, for example, 450 MHz from the RFpower source 111 is propagated through the coaxial line 108, the topelectrode, or antenna electrode 103 and the dielectric window 104, andintroduced into the process chamber. The electric field produced by theintroduced RF power in the chamber, and the magnetic field produced bythe field-producing coil 105 (for example, solenoid coil) in the chamberinteract with each other to generate a high-density plasma in thechamber. Particularly when the intensity of magnetic field produced inthe chamber is a value (for example, 160 G where the frequency ofplasma-producing RF power source is 450 MHz) that causes electroncyclotron resonance, the high-density plasma can be effectivelyproduced. Also, the RF power (of, for example, 800 kHz in frequency)from the antenna biasing power supply 114 is supplied through thecoaxial line 108 to the antenna electrode 103. Moreover, the RF power(of, for example, 800 kHz in frequency) from the substrate biasing powersupply 119 is supplied to the sample 116 placed on the substrateelectrode 115, so that the surface of the sample is processed (forexample, etched).

When the RF voltage from the antenna biasing power supply 114 is appliedto the antenna electrode 103 that is made of a desired material, thismaterial reacts with the radicals in the plasma, so that theconstituents of the produced plasma can be controlled. In the case of,for example, oxide film etching, if silicon Si is used for the materialof the antenna electrode 103, the amount of F-radical in the plasma canbe reduced that affects the etching characteristic on the oxide film, orparticularly the SiO₂/SiN selectivity.

In this apparatus, the plasma is produced chiefly by the RF power source111 of 450 MHz, the plasma constituents or plasma distribution iscontrolled by the antenna biasing power supply 114, and the energy ofions of the plasma incident to the sample 116 is controlled by thesubstrate biasing power supply 119. Thus, this apparatus has the meritthat the plasma generation (amount of ions) and plasma constituent(radical concentration ratio) can be independently controlled.

In general, a potential distribution may be formed on the sample to beprocessed by the influence of differences of plasma characteristic inthe surface, causing the charging damage in the plasma. If a voltage ofabout 5 V or above is applied across the gate oxide film of asemiconductor device having a film thickness of 4.5 nm, the gate oxidefilm is deteriorated. Therefore, in order to suppress the chargingdamage, it is necessary that the voltage across the gate oxide film bereduced to less than 5 V.

FIG. 2 is a graph showing the relation of the phase difference of the RFvoltages applied to the substrate electrode 115 and antenna electrode103 and the voltage developed across the gate oxide film. In FIG. 2, theordinate shows the voltage across the gate oxide film, and the abscissathe phase difference of the RF voltages. From FIG. 2, it will beunderstood that the voltage across the gate oxide film is about 6 V whenthe phase difference is around 0°, but can be restricted to as small asa tolerance or below when the phase difference is kept around 180°, orin the range of 180°±45°. If the phase difference is preferably in therange of 180°±30°, the voltage across the gate oxide film can be moreeffectively kept about 2 V or below.

FIGS. 3A and 3B are diagrams showing a substrate voltage waveform 301,an antenna voltage waveform 302 and a plasma potential waveform 303 whenthe phases of the RF voltages applied to the substrate electrode 115 andthe antenna electrode 103 are selected to be equal and opposite,respectively. From FIG. 3A, it will be seen that, when the voltages ofRF power are applied in phase, both substrate voltage waveform 301 andantenna voltage waveform 302 are sinusoidal. In addition, the plasmapotential waveform 303 has an oscillation of a large amplitude on thepositive potential side. On the other hand, as shown in FIG. 3B, whenthe voltages of the RF power are applied 180° out of phase, both voltagewaveforms 301, 302 are shifted to the negative voltage side, anddistorted to flatten on the positive voltage side. Thus, the plasmapotential waveform 303 is also flattened to still have a smallpotential. From the above facts, it will be understood that when the RFvoltages are applied 180° out of phase, the resulting self biaspotential is large, or increases as compared with the case when the RFvoltages are applied in phase.

The reason for this will be probably the fact that the electrodes thatare opposed to each other are improved in their earth function so thatenough currents can be supplied between both the electrodes. In otherwords, as shown in FIG. 4A, the antenna voltage waveform 302 of antennaelectrode 103 takes positive potential during a time t₁ in which theelectrons in the plasma are pulled in toward the antenna electrode, andnegative potential during a time t₂ in which the ions in the plasma arepulled in. On the contrary, the substrate voltage waveform 301 ofsubstrate electrode 115 takes negative potential during time t₁ in whichthe ions in the plasma are pulled in toward the substrate electrode, andpositive potential during time t₂ in which the electrons in the plasmaare pulled in. Therefore, since the plasma space has flow of currents(i₁, i₂) toward the substrate electrode during time t₁, and of currents(i₃, i₄) toward the antenna electrode during time t₂, sufficientelectrons are supplied when both the substrate electrode and the antennaelectrode are in phase to the positive voltage side, shifting it to thenegative voltage side. In addition, since those currents flow in thesame direction, either one of both the electrodes always effectivelyfunctions as an earth electrode to lower the plasma potential so thatthe plasma potential can be flattened to be low.

As shown in FIG. 4B, when the antenna voltage waveform 302 and thesubstrate voltage waveform 301 are applied in phase, the plasma spacehas flow of currents (i₁, i₂, i₃, i₄) in opposite directions toward theelectrodes, and thus the electric path is formed between the processchamber 102 grounded and each of the electrodes so that currents (t₅,i₆) flow to the inner wall of the chamber. As shown in FIG. 4C, if thesubstrate voltage waveform 301 of substrate electrode 115 remains thesame as in FIG. 4A, but if the antenna voltage waveform 302 of, forexample, 13.56 MHz in frequency is applied to the antenna electrode 103,a self-bias voltage V_(dc) is produced on the antenna electrode 103side, so that the ions in the plasma are always pulled in toward theantenna electrode. During time t₁, currents (i₁, i₂) flow in theopposite directions toward both electrodes. Therefore, an electric pathis formed between the process chamber 102 and each of the electrodes, sothat the current i₅ flows from the chamber side to both electrodes.During time t₂, the currents flow in the same direction toward theantenna electrode 103, but the difference (i₆) between the currentstoward the antenna electrode 103 and substrate electrode 115 flows tothe chamber 102 side.

Since more RF current flows between both the electrodes than to and fromthe side wall in the apparatus of this embodiment, the current flowingacross the magnetic field decreases, so that the charging damage can besuppressed from occurrence. Therefore, when the phase difference of RFvoltages to be applied to both electrodes is kept around 180° as shownin FIG. 2, the charging damage can be suppressed from occurrence, sothat the process for high yield can be carried out.

FIG. 5 is a graph showing the distributions of energy of ions incidentto both electrodes when the RF voltages to both electrodes are appliedin phase (0°) as indicated by a broken line (501) and 180° out of phaseas by a solid line (502). From FIG. 5, it will be understood that, whenthe RF voltages are applied 180° out of phase, the amount of ions isreduced in the low energy region but increases in the high energy regionas a result of shifting to a higher energy value as compared with thecase when the RF voltages are applied in phase. Although the energy ofions incident to the sample to be processed 116 is determined by theself-bias potential produced at the substrate electrode 115, the phasesof the RF power to the antenna electrode 103 and substrate electrode 115in this embodiment are made 180° out of phase as shown in FIG. 3B,thereby making it possible to increase the amount of high-energy ions asshown in FIG. 5. In other words, since the self-bias potential can befurther increased, the high-aspect-ratio holes can be processed withhigh precision performance. Moreover, the most appropriate etched shapecan be obtained by effective application of power.

In addition, the self-bias potential can be freely controlled even bycontrolling the phases of the RF power to the antenna electrode 103 andthe substrate electrode 115, and thus the range of the processingconditions can be widened.

FIG. 6 is a graph showing the relation of the ion saturated-currentdensity (as indicated by 601) measured on the outer periphery of thesubstrate electrode 115, and the phase difference between the RFvoltages. From FIG. 6, it will be understood that on the outer peripheryof the substrate electrode 115 the plasma density is high when the RFvoltages are applied in phase but low when the RF voltages are applied180° out of phase. That is, when the phase difference between the RFvoltages to the electrodes are made around 180°, either one of theelectrodes always efficiently serves as earth electrode, and thus theplasma potential can be suppressed from rising. As a result, thepotential difference between the plasma, and the inner walls of thegrounded process container 102 and vacuum vessel 101 decreases, so thatthe plasma produced inside the process container 102 is not expanded tothe inner walls of the process container 102 and vacuum vessel 101. Inother words, the plasma can be efficiently confined within the processcontainer 102.

The vacuum vessel 101 and process container 102 grounded are generallysputtered with the plasma, and the reaction products are attached ordetached to or from the inner walls thereof, thus acting as sources ofparticles that lowers the throughput. However, in this embodiment, sincethe plasma can be efficiently confined within the process container whenthe phase difference between the RF voltages are selected to be about180° as shown in FIG. 6, the reaction products can be suppressed frombeing attached to the inner walls of the vacuum vessel 101, and thevariation of the plasma potential 303 can be reduced as shown in FIG.3B. Therefore, the degree of sputtering by ion bombardment to the vacuumvessel 101 and process container 102 can be weakened. Thus, since thegeneration of particles from the vacuum vessel 101 and process container102 can be suppressed, the maintenance period of the apparatus can beextended, and the throughput can be improved.

In addition, according to this embodiment, a diverging magnetic fielddirected toward the substrate electrode 115 from the antenna electrode103 is produced within the process chamber by the field generation coil105. Thus, since the electrons in the plasma are moved under the controlof the magnetic field, the RF current flowing out of one electrodeefficiently flows toward the other opposite electrode rather thanflowing toward the side wall of the chamber. Therefore, the self-biasvoltage difference (δV_(dc)) can be reduced that is produced in thesurface of the substrate electrode in association with the chargingdamage. FIG. 7 is a graph showing the relation of the phase differenceof the bias voltages and the self-bias voltage difference between theself-bias voltages produced at the central and peripheral portions ofthe substrate electrode (δV_(dc)=V_(dc) at the center−V_(dc) at theperiphery) with the intensity of the magnetic field by the coil 105changed. From FIG. 7, it will be understood that there are values of thecoil current and values of the phase difference between the biasvoltages at which values the self-bias voltage difference (δV_(dc)) canbe made zero by increasing the current to the field-generating coil, orthe vertical component. Accordingly, if the vertical component of themagnetic field with respect to the sample to be processed 116 can bemuch produced in the chamber by the coil 105, the diffusion of theplasma can be effectively suppressed even if the distance between boththe electrodes is large (for example, 30 mm or above).

Also, even by using the field shape in which the field intensity isincreased as one proceeds toward the outer periphery from the center inthe process chamber, it is possible to suppress the electrons frommoving toward the outer periphery of the chamber. Therefore, the RFcurrent flowing out of one electrode flows toward the opposite electroderather than flowing toward the side wall of the chamber, and thus thesame effect can be achieved. This magnetic field can be produced even byuse of cusp field from an electromagnetic coil or cusp field from apermanent magnet.

The processing of the sample by the plasma in the above embodiment hasbeen described above. When the inner wall within the apparatus iscleaned by the plasma, the phase difference between the RF voltages tothe electrodes is made 0° (in phase), thereby making it possible todisperse the plasma widely and efficiently give bombardment of ions onthe wall, and thus the cleaning effect can be improved.

The same effects can be expected if the phases of the RF voltagesapplied to the antenna electrode 103 and substrate electrode 115 areopposite, or have a difference of about 180°±45°, preferably 180°±30° orif the phases of the RF voltages thereto are the same, or have adifference of about 0°±45°, preferably 0°±30°.

An example of the etching apparatus using magnetic field in thisembodiment has been described above. The present invention can also beapplied to an etching apparatus not using magnetic field, and otherplasma processing apparatus than the etching apparatus, such as ashingapparatus and plasma CVD apparatus in which RF power is supplied to thesubstrate electrode.

While the frequency of the RF voltages to the antenna electrode 103 andsubstrate electrode 115 in this embodiment is 800 kHz as describedabove, an RF power supply of a frequency at which the sheath becomesresistive, or about 5 MHz or below can be used to achieve the sameeffect.

Moreover, while the voltage signals are taken out of the junctions ofthe filters 112, 117 and the matching circuits 113, 118 in thisembodiment, they may be obtained from the output portions of thematching circuits 113, 118. Although the best effect can be achieved ifthe voltage signals for phase control are detected at the electrodes, inorder to remove other RF voltage noise it is desirable to detect them atleast through filters. In addition, since the phases of the RF voltagesat the output portions of the antenna biasing power supply 114 andsubstrate biasing power supply 119 are not coincident with those of theRF voltages at the electrodes 103, 115, it is desirable to detect themas near to the electrodes as possible.

Thus, according to the invention, by controlling the phases of the RFbias voltages applied to the substrate electrode and the electrodeopposite thereto, it is possible to reduce the current flowing betweeneach of both the electrodes and the inner wall of the vessel, to lowerthe potential difference of the potential distribution in the surface ofthe sample to be processed due to the distribution of the plasmacharacteristic in the surface, and thus to suppress the charging damagefrom occurring. Therefore, the yield of the sample can be improved.

In addition, since the energy of ions incident to the sample to beprocessed can be freely controlled by controlling the phases of the RFbias voltages, high-precision etching can be performed.

Also, since the plasma density near the inner wall of the vessel and thebombardment of ions to the wall can be more freely controlled bycontrolling the phases of the RF bias voltages, the occurrence ofparticles from the inner wall of the apparatus can be suppressed, andthus the cleaning period can be extended, leading to the improvement ofthroughput.

Furthermore, by controlling the phases of the RF bias voltages, it ispossible to make efficient cleaning within the vessel.

1. A plasma processing apparatus comprising: a container of which theinside is controlled to have a predetermined pressure-reducedatmosphere; a substrate electrode on which a sample to be processedprovided in said container can be placed; an antenna electrode providedto oppose said substrate electrode; a plasma-generating RF power supplyconnected via a first filter and a first matching circuit to saidantenna electrode to supply an R.F power thereto, for generating plasmawithin said container; an antenna biasing power supply connected via asecond filter and a second matching circuit to said antenna electrode; asubstrate biasing power supply connected via a third filter and a thirdmatching circuit to said substrate electrode; a phase controller forcontrolling a phase difference between biasing power supplied to saidantenna biasing electrode and biasing power supplied to said substrateelectrode to have a difference of 180°±45′; wherein said biasing powersupplied to the antenna biasing electrode and said biasing powersupplied to the substrate electrode have a same frequency, which samefrequency is lower than a frequency of said RF power for plasmageneration; wherein said first filter operates to pass RF power fromsaid plasma-generating RF power supply, but cut out RF biasing powerfrom said antenna biasing power supply; wherein said second filteroperates to pass biasing power from said antenna biasing power supply,but cut out RF biasing power from said plasma-generating RF powersupply; wherein said third filter operates to pass biasing power fromsaid substrate biasing power supply, but cut out RF power from saidplasma-generating RF power supply; wherein said phase controlleroperates to extract voltage waveforms from said second filter and saidsecond matching circuit and from said third filter and said thirdmatching circuit, respectively; wherein said phase controller controlsthe phase differences of the respective voltage waveforms within180°±45°, and signals with a small amplitude and a phase difference toeach other are output to said antenna biasing electrode and saidsubstrate biasing electrode.
 2. A plasma processing apparatus accordingto claim 1, comprising a magnetic generating coil for generating amagnetic flux passing through said antenna electrode and said substrateelectrode.